Publications
108 results found
Zhu Y, Vigil-Hernandez C, Kalha C, et al., 2023, Temperature-modulated solution-based synthesis of copper oxide nanostructures for glucose sensing, Materials Advances, Vol: 4, Pages: 3572-3582
Glucose sensors are widely applied in society as an effective way to diagnose and control diabetes by monitoring the blood glucose level. With advantages in stability and efficiency in glucose detection, non-enzymatic glucose sensors are gradually replacing their enzymatic counterparts and copper(ii) oxide (CuO) is a leading material. However, previous work extensively shows that even if the synthesis of CuO nanostructures is performed under nominally similar conditions, entirely different nanostructured products are obtained, resulting in varying physical and chemical properties of the final product, thereby leading to a differing performance in glucose detection. This work investigates the temperature dependence of a wet chemical precipitation synthesis for CuO nanostructures with the resulting samples showing selectivity for glucose in electrochemical tests. X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) demonstrate that all products are predominantly CuO, with some contribution from Cu(OH)2 and other surface species varying across synthesis temperatures. The most important change with increasing synthesis temperature is that the overall nanostructure size changes and the morphology shifts from nanoneedles to nanoparticles between 65 and 70 °C. This work helps to understand the critical relationship between synthesis temperature and final nanostructure and can explain the seemingly random nanostructures observed in the literature. The variations are key to controlling sensor performance and ultimately offering further development in copper oxide-based glucose sensors.
Snyder RM, Juelsholt M, Kalha C, et al., 2023, Detailed Analysis of the Synthesis and Structure of MAX Phase (Mo0.75V0.25)5AlC4 and Its MXene Sibling (Mo0.75V0.25)5C4., ACS Nano, Vol: 17, Pages: 12693-12705
MAX phases with the general formula Mn+1AXn are layered carbides, nitrides, and carbonitrides with varying stacking sequence of layers of M6X octahedra and the A element depending on n. While "211" MAXphases (n = 1) are very common, MAX phases with higher n, especially n ≥ 3, have hardly been prepared. This work addresses open questions regarding the synthesis conditions, structure, and chemical composition of the "514" MAX phase. In contrast to literature reports, no oxide is needed to form the MAX phase, yet multiple heating steps at 1,600 °C are required. Using high-resolution X-ray diffraction, the structure of (Mo1-xVx)5AlC4 is thoroughly investigated, and Rietveld refinement suggests P-6c2 as the most fitting space group. SEM/EDS and XPS show that the chemical composition of the MAX phase is (Mo0.75V0.25)5AlC4. It was also exfoliated into its MXene sibling (Mo0.75V0.25)5C4 using two different techniques (using HF and an HF/HCl mixture) that lead to different surface terminations as shown by XPS/HAXPES measurements. Initial investigations of the electrocatalytic properties of both MXene versions show that, depending on the etchant, (Mo0.75V0.25)5C4 can reduce hydrogen at 10 mA cm-2 with an overpotential of 166 mV (HF only) or 425 mV (HF/HCl) after cycling the samples, which makes them a potential candidate as an HER catalyst.
Westhead O, Spry M, Bagger A, et al., 2023, The role of ion solvation in lithium mediated nitrogen reduction, Journal of Materials Chemistry A, Vol: 11, Pages: 12746-12758, ISSN: 2050-7488
Since its verification in 2019, there have been numerous high-profile papers reporting improved efficiency of lithium-mediated electrochemical nitrogen reduction to make ammonia. However, the literature lacks any coherent investigation systematically linking bulk electrolyte properties to electrochemical performance and Solid Electrolyte Interphase (SEI) properties. In this study, we discover that the salt concentration has a remarkable effect on electrolyte stability: at concentrations of 0.6 M LiClO4 and above the electrode potential is stable for at least 12 hours at an applied current density of −2 mA cm−2 at ambient temperature and pressure. Conversely, at the lower concentrations explored in prior studies, the potential required to maintain a given N2 reduction current increased by 8 V within a period of 1 hour under the same conditions. The behaviour is linked more coordination of the salt anion and cation with increasing salt concentration in the electrolyte observed via Raman spectroscopy. Time of flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy reveal a more inorganic, and therefore more stable, SEI layer is formed with increasing salt concentration. A drop in faradaic efficiency for nitrogen reduction is seen at concentrations higher than 0.6 M LiClO4, which is attributed to a combination of a decrease in nitrogen solubility and diffusivity as well as increased SEI conductivity as measured by electrochemical impedance spectroscopy.
Jones LAH, Xing Z, Swallow JEN, et al., 2022, Band Alignments, Electronic Structure, and Core-Level Spectra of Bulk Molybdenum Dichalcogenides (MoS2, MoSe2, and MoTe2), JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 126, Pages: 21022-21033, ISSN: 1932-7447
Hariki A, Higashi K, Yamaguchi T, et al., 2022, Satellites in the Ti 1s core level spectra of SrTiO3 and TiO2, PHYSICAL REVIEW B, Vol: 106, ISSN: 2469-9950
Fernando NK, Bostrom HLB, Murray CA, et al., 2022, Variability in X-ray induced effects in [Rh(COD)Cl](2) with changing experimental parameters, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 24, Pages: 28444-28456, ISSN: 1463-9076
Jackson AJ, Parrett BJ, Willis J, et al., 2022, Computational Prediction and Experimental Realization of Earth-Abundant Transparent Conducting Oxide Ga-Doped ZnSb2O6, ACS ENERGY LETTERS, Vol: 7, Pages: 3807-3816, ISSN: 2380-8195
Morfill C, Pankratova S, Machado P, et al., 2022, Nanostars Carrying Multifunctional Neurotrophic Dendrimers Protect Neurons in Preclinical In Vitro Models of Neurodegenerative Disorders, ACS APPLIED MATERIALS & INTERFACES, Vol: 14, Pages: 47445-47460, ISSN: 1944-8244
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- Citations: 1
Xu Z, Thakur PK, Lee T-L, et al., 2022, Complex Magnetic Order in Topochemically Reduced Rh(I)/Rh(III) LaM0.5Rh0.5O2.25 (M = Co, Ni) Phases, INORGANIC CHEMISTRY, Vol: 61, Pages: 15686-15692, ISSN: 0020-1669
Fernando NK, Stella M, Dawson W, et al., 2022, Probing disorder in 2CzPN using core and valence states, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 24, Pages: 23329-23339, ISSN: 1463-9076
Ratcliff LE, Oshima T, Nippert F, et al., 2022, Tackling Disorder in γ‐Ga<sub>2</sub>O<sub>3</sub>, Advanced Materials, Vol: 34, ISSN: 0935-9648
<jats:title>Abstract</jats:title><jats:p>Ga<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> and its polymorphs are attracting increasing attention. The rich structural space of polymorphic oxide systems such as Ga<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> offers potential for electronic structure engineering, which is of particular interest for a range of applications, such as power electronics. γ‐Ga<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> presents a particular challenge across synthesis, characterization, and theory due to its inherent disorder and resulting complex structure–electronic‐structure relationship. Here, density functional theory is used in combination with a machine‐learning approach to screen nearly one million potential structures, thereby developing a robust atomistic model of the γ‐phase. Theoretical results are compared with surface and bulk sensitive soft and hard X‐ray photoelectron spectroscopy, X‐ray absorption spectroscopy, spectroscopic ellipsometry, and photoluminescence excitation spectroscopy experiments representative of the occupied and unoccupied states of γ‐Ga<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>. The first onset of strong absorption at room temperature is found at 5.1 eV from spectroscopic ellipsometry, which agrees well with the excitation maximum at 5.17 eV obtained by photoluminescence excitation spectroscopy, where the latter shifts to 5.33 eV at 5 K. This work presents a leap forward in the treatment of complex, disordered oxides and is a crucial step toward exploring how their electronic structure can be understood in terms of local coordination and overall structure.</jats:p>
Ratcliff LE, Oshima T, Nippert F, et al., 2022, Tackling Disorder in gamma-Ga2O3, ADVANCED MATERIALS, Vol: 34, ISSN: 0935-9648
Parvizian M, Duràn Balsa A, Pokratath R, et al., 2022, The Chemistry of Cu<sub>3</sub>N and Cu<sub>3</sub>PdN Nanocrystals**, Angewandte Chemie, Vol: 134, ISSN: 0044-8249
<jats:title>Abstract</jats:title><jats:p>The precursor conversion chemistry and surface chemistry of Cu<jats:sub>3</jats:sub>N and Cu<jats:sub>3</jats:sub>PdN nanocrystals are unknown or contested. Here, we first obtain phase‐pure, colloidally stable nanocubes. Second, we elucidate the pathway by which copper(II) nitrate and oleylamine form Cu<jats:sub>3</jats:sub>N. We find that oleylamine is both a reductant and a nitrogen source. Oleylamine is oxidized by nitrate to a primary aldimine, which reacts further with excess oleylamine to a secondary aldimine, eliminating ammonia. Ammonia reacts with Cu<jats:sup>I</jats:sup> to form Cu<jats:sub>3</jats:sub>N. Third, we investigated the surface chemistry and find a mixed ligand shell of aliphatic amines and carboxylates (formed in situ). While the carboxylates appear tightly bound, the amines are easily desorbed from the surface. Finally, we show that doping with palladium decreases the band gap and the material becomes semi‐metallic. These results bring insight into the chemistry of metal nitrides and might help the development of other metal nitride nanocrystals.</jats:p>
Kubitza N, Reitz A, Zieschang A-M, et al., 2022, From MAX Phase Carbides to Nitrides: Synthesis of V2GaC, V2GaN, and the Carbonitride V2GaC1-xNx, INORGANIC CHEMISTRY, Vol: 61, Pages: 10634-10641, ISSN: 0020-1669
Parvizian M, Balsa AD, Pokratath R, et al., 2022, The Chemistry of Cu3N and Cu3PdN Nanocrystals, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, Vol: 61, ISSN: 1433-7851
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- Citations: 3
McClelland I, El-Shinawi H, Booth SG, et al., 2022, The Role of the Reducible Dopant in Solid Electrolyte-Lithium Metal Interfaces, CHEMISTRY OF MATERIALS, Vol: 34, Pages: 5054-5064, ISSN: 0897-4756
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- Citations: 1
Xia Y, Ouyang M, Yufit V, et al., 2022, A cost-effective alkaline polysulfide-air redox flow battery enabled by a dual-membrane cell architecture, Nature Communications, Vol: 13, Pages: 1-13, ISSN: 2041-1723
With the rapid development of renewable energy harvesting technologies, there is a significant demand for long-duration energy storage technologies that can be deployed at grid scale. In this regard, polysulfide-air redox flow batteries demonstrated great potential. However, the crossover of polysulfide is one significant challenge. Here, we report a stable and cost-effective alkaline-based hybrid polysulfide-air redox flow battery where a dual-membrane-structured flow cell design mitigates the sulfur crossover issue. Moreover, combining manganese/carbon catalysed air electrodes with sulfidised Ni foam polysulfide electrodes, the redox flow battery achieves a maximum power density of 5.8 mW cm-2 at 50% state of charge and 55 °C. An average round-trip energy efficiency of 40% is also achieved over 80 cycles at 1 mA cm-2. Based on the performance reported, techno-economic analyses suggested that energy and power costs of about 2.5 US$/kWh and 1600 US$/kW, respectively, has be achieved for this type of alkaline polysulfide-air redox flow battery, with significant scope for further reduction.
Kalha C, Reisinger M, Thakur PK, et al., 2022, Evaluation of the thermal stability of TiW/Cu heterojunctions using a combined SXPS and HAXPES approach, JOURNAL OF APPLIED PHYSICS, Vol: 131, ISSN: 0021-8979
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- Citations: 1
Liu S, Ay A, Luo Q, et al., 2022, Oxidation of copper electrodes on flexible polyimide substrates for non-enzymatic glucose sensing, MATERIALS RESEARCH EXPRESS, Vol: 9
Balliou A, Papadimitropoulos G, Regoutz A, et al., 2022, Low-Cost, High-Gain MoS2 FETs from Amorphous Low-Mobility Film Precursors, ACS APPLIED ELECTRONIC MATERIALS, Vol: 4, Pages: 1175-1185
Kalha C, Ratcliff LE, Gutierrez Moreno JJ, et al., 2022, Lifetime effects and satellites in the photoelectron spectrum of tungsten metal, Physical Review B: Condensed Matter and Materials Physics, Vol: 105, Pages: 1-18, ISSN: 1098-0121
Tungsten (W) is an important and versatile transition metal and has a firm place at the heart of many technologies. A popular experimental technique for the characterization of tungsten and tungsten-based compounds is x-ray photoelectron spectroscopy (XPS), which enables the assessment of chemical states and electronic structure through the collection of core level and valence band spectra. However, in the case of tungsten metal, open questions remain regarding the origin, nature, and position of satellite features that are prominent in the photoelectron spectrum. These satellites are a fingerprint of the electronic structure of the material and have not been thoroughly investigated, at times leading to their misinterpretation. The present work combines high-resolution soft and hard x-ray photoelectron spectroscopy (SXPS and HAXPES) with reflected electron energy loss spectroscopy (REELS) and a multitiered ab initio theoretical approach, including density functional theory (DFT) and many-body perturbation theory (G0W0 and GW+C), to disentangle the complex set of experimentally observed satellite features attributed to the generation of plasmons and interband transitions. This combined experiment-theory strategy is able to uncover previously undocumented satellite features, improving our understanding of their direct relationship to tungsten's electronic structure. Furthermore, it lays the groundwork for future studies into tungsten-based mixed-metal systems and holds promise for the reassessment of the photoelectron spectra of other transition and post-transition metals, where similar questions regarding satellite features remain.
Offi F, Yamauchi K, Picozzi S, et al., 2021, Identification of hidden orbital contributions in the La0.65Sr0.35MnO3 valence band, PHYSICAL REVIEW MATERIALS, Vol: 5, ISSN: 2475-9953
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- Citations: 2
Fernando NK, Cairns AB, Murray CA, et al., 2021, Structural and electronic effects of X-ray irradiation on prototypical [M(COD)Cl](2) catalysts, The Journal of Physical Chemistry A: Isolated Molecules, Clusters, Radicals, and Ions; Environmental Chemistry, Geochemistry, and Astrochemistry; Theory, Vol: 125, Pages: 7473-7488, ISSN: 1089-5639
X-ray characterization techniques are invaluable for probing material characteristics and properties, and have been instrumental in discoveries across materials research. However, there is a current lack of understanding of how X-ray-induced effects manifest in small molecular crystals. This is of particular concern as new X-ray sources with ever-increasing brilliance are developed. In this paper, systematic studies of X-ray–matter interactions are reported on two industrially important catalysts, [Ir(COD)Cl]2 and [Rh(COD)Cl]2, exposed to radiation in X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) experiments. From these complementary techniques, changes to structure, chemical environments, and electronic structure are observed as a function of X-ray exposure, allowing comparisons of stability to be made between the two catalysts. Radiation dose is estimated using recent developments to the RADDOSE-3D software for small molecules and applied to powder XRD and XPS experiments. Further insights into the electronic structure of the catalysts and changes occurring as a result of the irradiation are drawn from density functional theory (DFT). The techniques combined here offer much needed insight into the X-ray-induced effects in transition-metal catalysts and, consequently, their intrinsic stabilities. There is enormous potential to extend the application of these methods to other small molecular systems of scientific or industrial relevance.
Fernando N, Cairns AB, Murray CA, et al., 2021, Structural and Electronic Effects of X-ray Irradiation on Prototypical [M(COD)Cl]2 Catalysts
<jats:p>X-ray characterisation techniques are invaluable for probing material characteristics and properties, and have been instrumental in discoveries across materials research. However, there is a current lack of understanding of how X-ray induced effects manifest in small molecular crystals. This is of particular concern as new X-ray sources with ever increasing brilliance are developed. In this paper, systematic studies of X-ray-matter interactions are reported on two industrially important catalysts, [Ir(COD)Cl]2 and [Rh(COD)Cl]2, exposed to radiation in X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) experiments. From these complimentary techniques, changes to structure, chemical environments, and electronic structure are observed as a function of X-ray exposure, allowing comparisons of stability to be made between the two catalysts. Radiation dose is estimated using recent developments to the RADDOSE-3D software for small molecules and applied to powder XRD and XPS experiments. Further insights into the electronic structure of the catalysts and changes occurring as a result of the irradiation are drawn from density functional theory (DFT). The techniques combined here offer much needed insight into the X-ray induced effects in transition metal catalysts and consequently, their intrinsic stabilities. There is enormous potential to extend the application of these methods to other small molecular systems of scientific or industrial relevance.</jats:p>
Fernando N, Cairns AB, Murray CA, et al., 2021, Structural and Electronic Effects of X-ray Irradiation on Prototypical [M(COD)Cl]2 Catalysts
<jats:p>X-ray characterisation techniques are invaluable for probing material characteristics and properties, and have been instrumental in discoveries across materials research. However, there is a current lack of understanding of how X-ray induced effects manifest in small molecular crystals. This is of particular concern as new X-ray sources with ever increasing brilliance are developed. In this paper, systematic studies of X-ray-matter interactions are reported on two industrially important catalysts, [Ir(COD)Cl]2 and [Rh(COD)Cl]2, exposed to radiation in X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) experiments. From these complimentary techniques, changes to structure, chemical environments, and electronic structure are observed as a function of X-ray exposure, allowing comparisons of stability to be made between the two catalysts. Radiation dose is estimated using recent developments to the RADDOSE-3D software for small molecules and applied to powder XRD and XPS experiments. Further insights into the electronic structure of the catalysts and changes occurring as a result of the irradiation are drawn from density functional theory (DFT). The techniques combined here offer much needed insight into the X-ray induced effects in transition metal catalysts and consequently, their intrinsic stabilities. There is enormous potential to extend the application of these methods to other small molecular systems of scientific or industrial relevance.</jats:p>
Kalha C, Fernando NK, Bhatt P, et al., 2021, Hard x-ray photoelectron spectroscopy: a snapshot of the state-of-the-art in 2020, JOURNAL OF PHYSICS-CONDENSED MATTER, Vol: 33, ISSN: 0953-8984
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- Citations: 39
Buschges MI, Hoffmann RC, Regoutz A, et al., 2021, Atomic Layer Deposition of Ternary Indium/Tin/Aluminum Oxide Thin Films, Their Characterization and Transistor Performance under Illumination., CHEMISTRY-A EUROPEAN JOURNAL, Vol: 27, Pages: 9791-9800, ISSN: 0947-6539
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Kalha C, Bichelmaier S, Fernando NK, et al., 2021, Thermal and oxidation stability of TixW1−x diffusion barriers investigated by soft and hard x-ray photoelectron spectroscopy, Journal of Applied Physics, Vol: 129, Pages: 1-15, ISSN: 0021-8979
The binary alloy of titanium-tungsten (TiW) is an established diffusion barrier in high-power semiconductor devices, owing to its ability to suppress the diffusion of copper from the metallization scheme into the surrounding silicon substructure. However, little is known about the response of TiW to high-temperature events or its behavior when exposed to air. Here, a combined soft and hard x-ray photoelectron spectroscopy (XPS) characterization approach is used to study the influence of post-deposition annealing and titanium concentration on the oxidation behavior of a 300 nm-thick TiW film. The combination of both XPS techniques allows for the assessment of the chemical state and elemental composition across the surface and bulk of the TiW layer. The findings show that in response to high-temperature annealing, titanium segregates out of the mixed metal system and upwardly migrates, accumulating at the TiW/air interface. Titanium shows remarkably rapid diffusion under relatively short annealing timescales, and the extent of titanium surface enrichment is increased through longer annealing periods or by increasing the bulk titanium concentration. Surface titanium enrichment enhances the extent of oxidation both at the surface and in the bulk of the alloy due to the strong gettering ability of titanium. Quantification of the soft x-ray photoelectron spectra highlights the formation of three tungsten oxidation environments, attributed to WO
Moss B, Wang Q, Butler K, et al., 2021, Linking in situ charge accumulation to electronic structure in doped SrTiO3 reveals design principles for hydrogen-evolving photocatalysts, Nature Materials, Vol: 20, Pages: 511-517, ISSN: 1476-1122
Recently, high solar-to-hydrogen efficiencies were demonstrated using La and Rh co-doped SrTiO3 (La,Rh:SrTiO3) incorporated into a low-cost and scalable Z-scheme device, known as a photocatalyst sheet. However, the unique properties that enable La,Rh:SrTiO3 to support this impressive performance are not fully understood. Combining in situ spectroelectrochemical measurements with density functional theory and photoelectron spectroscopy produces a depletion model of Rh:SrTiO3 and La,Rh:SrTiO3 photocatalyst sheets. This reveals remarkable properties, such as deep flatband potentials (+2 V versus the reversible hydrogen electrode) and a Rh oxidation state dependent reorganization of the electronic structure, involving the loss of a vacant Rh 4d mid-gap state. This reorganization enables Rh:SrTiO3 to be reduced by co-doping without compromising the p-type character. In situ time-resolved spectroscopies show that the electronic structure reorganization induced by Rh reduction controls the electron lifetime in photocatalyst sheets. In Rh:SrTiO3, enhanced lifetimes can only be obtained at negative applied potentials, where the complete Z-scheme operates inefficiently. La co-doping fixes Rh in the 3+ state, which results in long-lived photogenerated electrons even at very positive potentials (+1 V versus the reversible hydrogen electrode), in which both components of the complete device operate effectively. This understanding of the role of co-dopants provides a new insight into the design principles for water-splitting devices based on bandgap-engineered metal oxides.
Hartley P, Egdell RG, Zhang KHL, et al., 2021, Experimental and Theoretical Study of the Electronic Structures of Lanthanide Indium Perovskites LnInO(3), JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 125, Pages: 6387-6400, ISSN: 1932-7447
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- Citations: 5
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